Provides evidence that multilingual CLIL has a positive effect on productive vocabulary. This book fills an important gap in the literature by providing evidence of the positive effect that receiving content classes in multiple target languages has on vocabulary acquisition and, in particular, lexical availability. It examines data from a multilingual Content and Language Integrated Learning (CLIL) context, where Spanish adolescents simultaneously study both English and French as foreign languages. The author explores the quantitative and qualitative differences between CLIL learners' language acquisition in English and French and between males and females, as well as the positive and negative influence of the learners' various languages in their available lexicon. In addition, these factors are investigated not only at one point in time, but also longitudinally, so as to address the long-term effects of these issues. The book equips teachers and stakeholders with clear information regarding the effect that multilingual CLIL instruction has, to allow them to make the most of this multilingual learning scenario and foster the learners' multilingual exposure.